A circuit may be used to bias other components or circuits. For example, a circuit may generate a bias current and provide it to a component to establish the proper mode of operation of the component. As a particular example, a bandgap circuit may be used to provide a bias current to analog components, such as an amplifier. A constant and precise bias current allows these components to perform at their intended range of operation.
Existing bandgap circuits may be formed from diodes and take advantage of the Arrhenius dependence of current in a diode to generate currents and voltages that are proportional to the absolute temperature. Generally, existing bandgap circuits are used to generate a temperature-independent voltage which is then passed to an external precision resistor to convert this voltage into a temperature-independent current for use by components such as amplifiers. Due to packaging and other design constraints, it may be undesirable to dedicate two pins of a package to the generation of such a temperature-independent current.
Current in a diode is proportional to its area. Generally, existing bandgap circuits utilize diodes that are biased well above their turn-on voltages of approximately 0.7 Volts (V). Advances in process and fabrication technologies have led to the introduction of circuits and components having lower supply voltages. At lower supply voltages, many bandgap circuits which utilize diodes are not practical because it is difficult to generate the required voltage drop. Existing bandgap circuits are not suited for use in systems which have supply voltages in the range of 1V and lower, unless large amounts of valuable substrate area are allocated to the fabrication of the diodes.